Does measuring the spin of a Particle Randomize it's spin for the future? How is this compatible with verification of Quantum Entanglement

I am super confused about this. I thought that for an entangled particle if you measure the spin of one, the whole system should get randomized (as both particles are inherently connected and the state of one has been measured). How do we know the unmeasured particle is actually the opposite spin? All the explanations I read is when we measure the spin of 1 particle we automatically know the spin of the entangled particle is opposite, but how can this be verified when measuring the spin of the first should have randomized the whole system? Without verification we can't get the "spooky action at a distance" phenomenon so there has to be a way to measure both particles and then compare their states but this doesn't make sense to me as measuring one should have randomized the other.